If you've been following the world of quantum science, you've probably seen the example of quantum entanglement shared between "Alice and Bob." If Alice has a particle entangled with one of Bob's particles and Bob teleports it to "Charlie, "Alice's particle becomes entangled with Charlie's. (Google the words Bob, Alice and quantum teleportation to learn more about this.)

This example has been used for years, but physicists at the Institute for Quantum Computing (IOC) at the University of Waterloo have demonstrated the distribution of three entangled photons at three different locations (Alice, Bob and Charlie) several hundreds of meters apart. This three photon entanglement leads to some interesting possibilities for multi-party quantum communication.

"The interesting result is that we now have the ability to do more than paired quantum communication. QKD, so far, has been a pair-wise system--meaning that it works best and with less assumptions when you’re only talking with one other person," said Chris Erven, a former IOC PhD student who is now a research assistant at the University of Bristol. "This is the first experiment where you can now imagine a network of people connected in different ways using the correlations between three or more photons."

(Erven is the lead author of the paper "Experimental Three-Particle Quantum Nonlocality under Strict Locality Conditions" published in Nature Photonics on March 23 this year.)

The experiment opens the possibility for multipartite quantum communication protocols, including Quantum Key Distribution (QKD), third-man cryptography and quantum secret sharing. Co-author Professor Kevin Resch, Canada Research Chair in Optical Quantum Technologies, observed: "Correlations measured from quantum systems can tell us a lot about nature at the most fundamental level. Three-particle entanglement is more complex than that of pairs. We can exploit the complex behavior to rule out certain descriptions of nature or as a resource for new quantum technologies."

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